How to access isispConfig3 websites created without domain names

Hi,
I'm a total newbie with ispConfig that I got installed on an ovh dedicated server.
I bought the doc.pdf where it is said that I should be able to access freshly created websites but at whitch url ?
When I try http://ip_or_name_server/testsite.com/web/ I get 403 error with "client denied by server configuration: /var/www/testsite.com/web/index.html" in apache logs

I need that feature to test websites before real domain name transfers.

The purpose of the /etc/hosts file is to override domains in DNS. So if you set the domain in the hosts file (on your desktop, not the server!), then it instructs your browser to access the server that is defined in /etc/hosts and to ignore the DNS record. Just try it, you will see then that it works for Linux, *BSD, Windows and MacOS.